A typical blood circuit that is used in dialysis treatment as a blood purification treatment and through which the blood of a patient is extracorporeally circulated basically includes an arterial blood circuit to one end of which an arterial puncture needle is attached, and a venous blood circuit to one end of which a venous puncture needle is attached. A dialyzer serving as a blood purifier is connectable to the other respective ends of the arterial blood circuit and the venous blood circuit. The arterial blood circuit is provided with a peristaltic blood pump. When the blood pump is activated with the arterial puncture needle and the venous puncture needle being stuck in the patient, blood is collected through the arterial puncture needle. Furthermore, the collected blood is caused to flow through the arterial blood circuit and is introduced into the dialyzer, where the blood is purified. The purified blood is further caused to flow through the venous blood circuit and is returned into the body of the patient through the venous puncture needle. Thus, the dialysis treatment is performed.
The known blood circuit that performs the above extracorporeal circulation is provided with a medical liquid-pressure-detecting device for detecting the pressure of liquid such as blood (see PTL 1, for example). Such a known medical liquid-pressure-detecting device includes a diaphragm that is deformable in accordance with pressure change that occurs when a negative pressure or a positive pressure is generated in the liquid. The medical liquid-pressure-detecting device is capable of detecting the pressure of the liquid on the basis of the pressure change in a gas that occurs with the deformation of the diaphragm. The diaphragm has an arc shape that is concave either on the liquid side or on the gas side. If the arc shape projects on the gas side, a sensor for negative-pressure detection capable of detecting negative pressure is provided. If the arc shape projects on the liquid side, a sensor for positive-pressure detection capable of detecting positive pressure is provided.
PTL 1: U.S. Pat. No. 8,092,414 the teachings of which are incorporated by reference herein for all purposes.